1. Field of the Invention
This invention generally relates to flexible shaft couplings having a yielding element, and more particularly to a torsionally resilient shaft coupling for serially transmitting torque and to provide a substantial amount of torsional flexibility between a pair of axially spaced and coaxially aligned shafts.
2. Description of the Prior Art
Torsionally resilient shaft couplings are typically used in industry to provide torsional flexibility between a driving member and a driven member. Typically, torsionally resilient shaft couplings are used in main drive systems connecting motors to rolls, used in metal rolling mills for reducing the thickness of metal plates. In such rolling mill drive systems, high impact shock loads excite vibration frequencies when a metal plate enters between the rolls to be reduced in thickness. Without some sort of torsional flexibility within the drive system, the tremendous shock loads encountered and the great amount of torque needed to keep the rolls turning as it reduces the thickness of the metal strip, would damage the drive system. Thus, it is common that shaft couplings are used to provide most of the needed torsional flexibility.
In a typical steel rolling mill the large main rolling mill drive usually comprises an electrical motor coupled to a spacer coupling which is coupled to a pinion stand and a pair of spindle couplings connect the pinion stand to the rolls. In some applications, a conventional Holset type coupling, such as shown in Croset U.S. Pat. No. 2,873,590, may be used in the drive system to give the necessary torsional flexibility to sufficiently reduce the vibrational response of the system so that damage to the drive system is lessened. However, where very high torque applications are encountered such as in the large drive systems of main steel rolling mills, a Holset type coupling large enough to transmit the torque and yet provide the necessary torsional flexibility to adequately reduce the vibration would be excessively large, unwieldly and expensive.
In the main drive system, the spacer coupling is the logical place to provide for torsional flexibility. Generally, the spacer coupling comprises a pair of conventional misalignment gear type coupling halves which are coupled together by a spacer which may extend between 10 and 30 feet in length and may also extend through a dividing wall which separates the electrical motor and the pinion stand. It would be convenient to replace the spacer between the two coupling halves with a torsionally resilient shaft coupling that will transmit a great amount of torque while at the same time have a high degree of torsional flexibility to reduce the vibration that would otherwise be encountered.
Several torsionally flexible shaft couplings are shown in Hartz et al. U.S. Pat. No. 2,910,843, Crankshaw U.S. Pat. No. 3,080,732, and Strasburg et al. U.S. Pat. No. 3,834,181. Each of the above torsionally flexible shaft couplings are designed to transmit a high amount of torque while at the same time providing some degree of torsional flexibility. In each of the three above prior art patents, the torsionally flexible shaft coupling includes an inner sleeve connected at one end to a driven apparatus, an outer sleeve surrounding the inner sleeve providing a space therebetween, and connected to a driving apparatus. A plurality of torsionally flexible members are then interposed between the outer and inner sleeve. Each one of the torsional members include a pair of axially separated plates of which one plate is splined to the outer sleeve and the other plate is splined to the inner sleeve. Interposed between the two plates and bonded thereto is a flexible yielding element. Thus, torque is transmitted from the driving member through the outer sleeve through the flexible member to the inner sleeve and then out to the driven apparatus.
Although the above three couplings transmit a great amount of torque they do have limited usefulness where, in addition to a great amount of torque, a high degree of torsional flexibility, that is a low torsional stiffness, is desired. The more individual flexible elements that are placed in parallel between the outer sleeve and the inner sleeve will cause an increase in the amount of torque that will be transmitted but the torsional stiffness of the coupling also increases thus decreasing the torsional flexibility. Thus, as shown in the Strasburg et al patent, Hartz et al patent, and Crankshaw patent only a limited number of individual flexible elements can be used in parallel if a low torsional flexibility is of prime importance.
By placing a number of these flexible units in parallel as shown in Crankshaw, Hartz et al., and Strasburg et al. the amount of torque to be transmitted is increased, however, the torsional stiffness is also increased. Thus, where a higher degree of torsional flexibility is desired in addition to a high amount of torque transmission, the above three prior art patents would be inadequate because they are incapable of performing both functions.